Fire warning cable



Aug. 13, 1968 L. R. sPlcr-:R

FIRE WARNING CABLE 2 Sheets-Sheet 1 Filed Dec. 28, 1966 Inventor L YNDONR. SP/CER 13g/Of A Morne y Aug.13,196s RSPICER 3,397,313

FIRE WARNING CABLE 'Filed nee. 2e, 196e 2 sheets-sheet 2 nveplor LYNDQNR. SPICE@ ,BOrOz/' Attorney United States Patent O 3,397,373 FIREWARNING CABLE Lyndon Reginald Spicer, Cascades, Llandevaud, Wales,

ABSTRACT OF THE DISCLOSURE A cable for a re warning system in which apair of conductors are covered by insulation having gaps to expose theconductors. Low melting point slugs of conductive material overlie thegaps and are encased in an elastic sleeve which when the slugs aremelted force -them in-to the gaps to form a conductive path between theconductors.

Summary of invention This invention relates to cables for use in rewarnin-g systems, and to methods of manufacturing such cables.

According to the present invention there is provided a cable for use ina tire warning system comprising two insulated conductors, an aplurality of slugs of material having a low melting point, said slugsbeing spaced apart along the length of the cable, wherein each slug isso arranged that on reaching its melting point it provides anelectrically conductive path between said two conductors.

According to the present invention there is further provided a cable foruse in a re warning system comprising two insulated conductors, aplurality of slugs of material having a low melting point, said slugsbeing spaced apart along the length of the cable, and .meansindividually :associated with each one of the slugs for causing theassociated slug on reaching its melting point to provide an electricallyconductive path between said two conductors.

According to one aspect 'of the present invention there is provided amethod of manufacturing such cables.

Description of drawings FIGS. 1 and 2 are a side view and -a crosssection respectively illustrating a lirst embodiment,

FIG. 3 is a cross section of a second embodiment;

FIGS. 4a and 4b are a side view and an exploded view respectively of athird embodiment;

FIG. 5 illustrates steps in the manufacture of the ythird embodiment.

Description of the preferreld embodiments The embodiment illustrated inFIGS. 1 and 2 employs a cable consisting of two parallel coppercladsteel conductors 1 and 2 and a polyvinyl chloride insulating cover 3havingtwo at surfaces. In a preferred embodiment the polyvinyl chloridecover has a height of 0.017 inch between the at surfaces, and themaximum perpendicular diameter is 0.15 inch. The conductors are exposedby gaps 4 in the polyvinyl chloride cover which occur, for example, atintervals of .three feet along the length of the cable. A Suitable widthfor each gap is 3/16 inch. Slugs 5 of an alloy having a low meltingpoint bridge the gaps in the polyvinyl chloride cover, and each slug isheld in place by an elastic, e.g. rubber, sleeve. Suitable examples ofalloys having a low melting point are Cerrobend RTM which has a meltingpoint in a range from 70 C. and above, and Woods metal. The compositionof the latter alloy can be varied to obtain melting points in the range117 F. to 302 F., in one form it l' 3,397,373 Ice Patented Aug. 13, 1968consists of 50% bismuth, 13% cadmium, 25% lead and 12% tin. In oneembodiment the slug has a length of 0.3 inch, a width of 0.15 inch and athickness of 0.05 inch. The cable together with the slugs can besheathed with out melting the alloy.

When the temperature of a slug reaches the melting point of the alloy,the rubber sleeve contracts over the now pliable slug and forces thealloy into the adjacent gap in the polyvinyl chloride cover, so that thetwo.

conductors are short circuited. Where less consistent action can betolerated, the elastic sleeve may be replaced by some other retainingdevice and the effect of gravity on the melted slug be used to providean electrically conductive path between the two conductors.

FIG. 3 is a cross sectional View of a second embodiment employing acoaxial cable with conductors 6 and 7. The inner conductor `6 is exposedat intervals of e.g. 3 ft. along the length of the cable 'by gaps 8 inthe outer conductor 7 and any insulation between the outer and innerconductors. A suitable width for each gap is again IAG inch. Each gap isbridged by a tubular slug of alloy 9 having a length of 0.3 inch, anexternal diameter of 0.1 inch and an internal diameter of 0.05 inch.Copper braid 10 surrounds the external conductor together with theslugs, and rubber sleeves 11 are placed over the copper braid, oneadjacent to each alloy slug. The entire arrangement is covered by apolyvinyl chloride sheath 12.

To facilitate main production by automatic or semiautomatic techniques,there is provided a further embodiment of the means individuallyassociated with each one of the slugs to cause the associated slug onreaching its melting point to provide an electrically conductive pathbetween the two conductors.

FIGS. 4a and 4b are a side view and an exploded view respectively of afourth view of the invention. A cable 13, similar to that of FIGS. 1 and2 is provided with gaps 14 at intervals along its length which havesimilar dimensions to the gaps 4 of FIG. l. Metallic, e.g. aluminiumplates 15 crimped around the lgaps 14 are each provided with a punchedrecess 16 Iopposite the gap 14. The recesses 16 are loaded withresilient, e.g. rubber pads 17 and low melting point alloy slugs 18, therubber pads being compressed against the slugs, and the latter bridgingthe gaps 14.

When the temperature of a slug reaches the melting point of the alloys,the compressed rubber pad forces the now pliable slug into the adjacentgap 14, so that the two conductors are short circuited.

FIG. 5 illustrates successive stages in the manufacture of FIG. 4. Instage (i) of the manufacture, a recess 19 is punched in an initiallycontinuous aluminium strip 20 which is moving in lthe direction of thearrow. In stage (ii) a rubber pad 21 is blanked from a strip of rubberand drives into the recess 19. Simultaneously another recess 22 ispunched on the strip at the first point of the production line. Next(stage iii) a low melting point alloy slug 23 is blanked from a stripand driven into the recess 19 over the rubber pad 21. Stages l and 2 arerepeated for each recess. The assembled unit is separated from the4strip of -aluminium stage (iv) and the aluminium surrounding the unitis preformed into a U-shaped member 24. In stage (v) a slot 14 in acable 13 is located over the alloy slug 23 and the preformed aluminiumis crimped round the cable to form a sleeve 25 so that the rubber pad iscompressed against the alloy slug. Previous stages are repeated in eachof stages (iv) and (v).

It is to be understood that the foregoing description of specic examplesof this invention is made by way of example only and is not .to beconsidered as a limitation on its scope.

I claim:

1. A cable for use in a fire warning system comprising:

lat least -two conductors surrounded by insulating material having aplurality of gaps provided along the length of the insulation toperiodically expose said conductors relative to each other;

ya plurality of slugs of material having a low melting point and eachbeing positioned yto bridge said plurality of gaps;

a resilient member compressed against each of said slugs for `causingthe associated slug on reaching its melting point to deform into saidgap 'and provide an electrically conductive path between said twoconductors; and

means surrounding and maintaining said slug and its associated resilientmember in proper position with respect to the associated gap.

2. A cable according to claim 1 wherein said cable is a coaxial cablehaving its inner conductor exposed to the surrounding outer conductorthrough the gap in the insulation surrounding said inner conductor andthrough a gap in the outer conductor, and each of said slugs bridges oneof said gaps in the outer conductor.

3. A cable according to claim 2 further including an elastic sleevestretched over the portion of the cable which includes one of said slugsbridging one of said gaps in the -outer conductor, -and an insulatingcover sur-rounding said sleeve and outer conductor.

4. A cable according to claim 1 wherein said two conductors are parallelinsulated conductors which are periodically exposed by said gaps, eachof said gaps is bridged by said slug and a resilient pad compressedagainst said slug, and means are provided at each of said gaps forlocating and maintaining said slug and resilient pad in the properposition.

5. A cable according to claim 4 wherein said locating and maintainingmeans is a metallic plate crimped around said cable and provided with Iarecess for said resilient pad and slug.

6. A cable according to claim 5 wherein the material of said slug is anelectrically conductive metal alloy.

7. A coaxial cable for use in a re warning system comprising:

an insulated inner conductor having a plurality of gaps spaced along thelength of the insulation to` expose the inner conductors;

an outer conductor surrounding said insulated inner conduct-or andhaving coincident gaps in its surface;

a slug of material of low melting point bridging each of said gaps;

an elastic sleeve stretched over said slug for casing said slug onreaching itsrmelting kpoint tb'deform into said gap and to provide an4electiaca'lly `con ductive path between said inner. and` outerconductor; and

van insulating cover completely surrounding said outer conductor andsleeve. l

8. A cable for use in a fire warning system comprising:

a pair of parallel conductors surrounded byf 'an insulating cover havingla plurality of gaps spaced along the length of the insulation to exposesaid conductors;4

a slug of material having a 10W melting point bridges each of said gap;

a resilient pad is compressed against said slug causing' said slug onreaching its melting point to deform into the associated gap and providean electrically conf References Cited UNITED STATES PATENTS 1,109,8789/1914 Sulzbacher 200-143 1,829,149 1'0/ 1931 Mason et al. 200--1433,294,941 12/ 1966 Mullen `200--143 3,305,625 2/1967 Ellis 200-1743,316,343 4/1967 Sherlock 200-174 BERNARD' A. GILHEANY, PrimaryExaminer.

H. B. GILSON, Assistant Examiner.

